Analysis of surface roughness in Ti/Al/Ni/Au Ohmic contact to AlGaN/GaN high electron mobility transistors

A mechanism of the formation of the bulges on the surface of Ti/Al/Ni/Au Ohmic contact in AlGaN/GaN high electron mobility transistors is proposed. According to the analysis of TEM images and corresponding electron dispersive x-ray spectra, the bulges were found to consist of Ni–Al alloy in the body and Au–Al alloy surrounding. We deduce that the bulges were formed due to Ni–Al alloy aggregation in some local areas during the rapid thermal annealing process, which accounts for the rough surface morphology.

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